Silica-Supported Au–CuOx Hybrid Nanocrystals as Active and Selective Catalysts for the Formation of Acetaldehyde from the Oxidation of Ethanol

The selective oxidation of ethanol with molecular O2 is increasingly becoming an important process to develop fine chemicals because it can be obtained from renewable biomass feedstock while reducing the demand on fossil fuels. We have synthesized silica-supported Au–Cu alloy nanoparticles, and through an oxidative dealloying process, we have developed Au–CuOx hybrid catalysts for the selective oxidation of ethanol into acetaldehyde. Using a combination of XRD, XPS, and HR-STEM experiments, we have confirmed that the active catalyst is a Au core with a thin CuOx shell. Oxidation of the AuCu/SiO2 alloy catalyst at 300 °C was found to produce the most active and stable catalyst for ethanol conversion (∼90%) with the highest selectivity (∼80–90%) at a reaction temperature of 200 °C for 50 h on-stream. TEM and XRD results show that Au–CuOx/SiO2 catalysts calcined at 300 and 500 °C are also more resistant to sintering during pretreatment and catalytic conditions than pure gold supported on silica. Furthermore, the silica-supported Au–CuOx catalysts (calcined at 300 and 500 °C) were also found to be more active and selective in the dehydrogenation of ethanol to form acetaldehyde. It is likely that the increased interfacial contact between the Au and CuOx forms the most active site on the catalyst and is responsible for the enhanced catalytic properties when compared with pure Au/SiO2.